The present invention relates to hearing aid systems, and more particularly to a hybrid or Electro Acoustic Stimulation (EAS) hearing aid system that combines a cochlear stimulator and a hearing aid to provide a hearing aid system that relies primarily on the cochlear stimulator portion of the system for being able to sense high frequency sounds, and that relies primarily on normal hearing processes, assisted as required by a hearing aid, for being able to sense lower frequency sounds. A representative hybrid or EAS hearing system is described, e.g., in U.S. Pat. No. 6,754,537, incorporated herein by reference in it's entirety.
A hybrid or EAS hearing aid system, such as is disclosed in U.S. Pat. No. 6,754,537, is best suited for use with a short cochlear electrode array of the type described in U.S. Pat. No. 6,889,094 entitled “Electrode Array for Hybrid Cochlear Stimulator”, or equivalent short, atraumatic lead. U.S. Pat. No. 6,889,094 is incorporated herein by reference.
A hybrid or EAS cochlear stimulation system provides electrical stimulation only to the basal end of the cochlea to stimulate ganglion cells responsible for sensing higher-frequency sounds, and relies on normal or assisted hearing (activation of hair cells through fluid motion within the cochlea), which may occur with or without the assistance of a conventional or a custom hearing aid, to sense middle-to-lower frequency sounds.
A common problem that plagues hearing aid users is feedback. Feedback occurs in an acoustic amplification system, such as a hearing aid system, when the amplified sound is picked up by the microphone, causing the amplification system to become unstable and squeal. The best way to eliminate feedback is to acoustically separate the microphone from the hearing aid “speaker”, or electrical-to-acoustic transducer used to broadcast amplified audio signals against the user's ear drum. However, despite efforts to seal the ear canal (e.g., by preparing an ear mold designed to fit tightly in the ear canal with the microphone held on the side of the mold facing the outside of the ear, and the speaker held on an opposite side of the mold facing the ear drum, with the intent of acoustically separating the speaker from the microphone), some acoustic sound waves broadcast from the speaker always seem to leak back to the microphone, where they are sensed by the microphone, causing the hearing aid system to become unstable and squeal.
Thus, it is seen that there is a need in the art for eliminating feedback in a hearing aid system, and more particularly for eliminating feedback in an EAS hearing prosthesis system utilizing both a cochlear implant for allowing a user to perceive high frequency sound, and a conventional hearing aid for allowing the user to hear low frequency sound.